Field of the Invention
The present invention relates to an electronic device and a method for controlling an electronic device.
Description of the Related Art
As a display monitor on a mobile communications terminal, such as a smartphone, or a digital camera, a liquid crystal monitor equipped with a touch panel is used. For example, a capacitive touch panel that supports multi-touch or gesture operations is often mounted. In a liquid crystal monitor equipped with a touch panel, the touch panel is arranged on the display surface side of the liquid crystal monitor, as illustrated in FIG. 6. In FIG. 6, a liquid crystal monitor is illustrated that includes a touch panel 601, a thin-film transistor (TFT) panel 602 of the liquid crystal monitor (display), and a backlight 603 of the liquid crystal monitor.
In this configuration, the touch panel is arranged above the liquid crystal monitor. As a result, the touch panel is affected by noise caused by driving of the liquid crystals and driving of the backlight. In particular, for an in-cell touch panel or an on-cell touch panel, those effects are substantial due to the touch panel being arranged above liquid crystal electrodes or above a color filter without a glass sheet or a film being arranged between the touch panel and the liquid crystal electrodes or the color filter.
As the backlight of the liquid crystal monitor, a white light-emitting diode is mainly used. The emitted brightness is determined based on a value of the current flowing to the white light-emitting diode. There are two methods of controlling the current of a light-emitting diode, namely, a method for controlling the current value by a direct current, and a method called pulse width modulation control (PWM control), in which the current value of the direct current is fixed and a timing at which current flows is controlled based on a pulse width. When direct current control is performed, the color hue of the white light-emitting diode changes based on the current value. Therefore, for a monitor to be used to confirm on the monitor an image taken by a digital camera, PWM control is often performed in order to prevent the color hue from changing depending on the brightness.
However, in PWM control, noise is produced due to the switching that is repeatedly performed in order to turn the backlight current on and off. This noise affects the touch panel. When a capacitance detection frequency of the touch panel for detecting an operation on the touch panel and a PWM drive frequency of the backlight current match, the effects of this noise are increased, which can cause an output signal of the touch panel to fluctuate, resulting in erroneous detection of an operation.
For example, in Japanese Patent Application Laid-Open No. 2013-235197, a technology is disclosed in which noise caused by driving of the backlight is reduced by synchronizing touch detection of the touch panel and driving of the backlight.
However, in the technology disclosed in Japanese Patent Application Laid-Open No. 2013-235197, backlights need to be arranged parallel to a region at which touch detection of the touch panel is performed. Further, control for synchronizing touch detection of the touch panel and driving of the backlights needs to be performed for each backlight that is connected in parallel, and hence the touch detection of the touch panel and the control of the backlights are more complex.